1. Field of the Invention
The invention relates generally to fire detection systems having remote stations coupled to a central analysis station and particularly to a fire detection system having optical fibers which transmit flame signals from remote sensing stations to a central detection and analysis station.
2. Description of the Prior Art
Conventional fire detection and alarm systems take a variety of forms, those systems utilizing a number of monitors scattered throughout a facility which is to be protected being of particular interest relative to the present improvement. In such systems, each of the remote monitors effectively constitutes a flame detector and contains either an ionization chamber or light sensitive cell in association with optical subsystems, each monitor acting to produce an electrical output which is transmitted as an electrical signal by appropriate wire or cable connections to a central analysis subsystem within which the electrical signals are analyzed and a warning signal generated when analysis shows the detection of a fire by one of the monitors. These conventional fire detection systems accordingly require the use of a transistor at each monitoring location in addition to associated optics and mounting hardware along with ancillary electrical components for conversion of a light signal to an electrical signal at the remove monitoring location. Additionally, metal conduits are required to encase the wire or cable along which electrial signals are transmitted from each monitor to the central analysis subsystem, this shielding being necessary in order to prevent EMI/RFI interference, a primary consideration due to the fact that output from the transducers are of low magnitude. Shielding of the wire or cable connectors as well as the flame detection apparatus at each monitor is necessary in order to prevent damage caused by fire extinguishing fluids which can cause corrosion and other damage which result in false signals and contribute to defective flame detection operation. Substantial expense is thus involved in shielding and sealing the relatively long wiring runs and in sealing each monitor in order to prevent contact between these elements of the system and fire extinguishing fluids. Substantial expense is also incurred in these prior art systems by virtue of the fact that each of the remote monitors actually constitutes a flame detector in and of itself and thus requires that a transducer and associated apparatus constitute each monitor.
Exemplary of issued United States patents which relate to optical systems for spectral analysis of incident electromagnetic radiation, such as can be used in the detection of fires, are patents such as U.S. Pat. No. 4,037,113 to Moore which discloses the detection of flames in a boiler by the disposition of bundles of fiber optics in openings formed in the boiler, the optical fibers feeding incident light to respective photodetectors. Louder et al, in U.S. Pat. No. 3,885,879, discloses a spectrophotometer which utilizes an adjustable spectral wedge interposed between a light source and a photosensitive apparatus for selecting wavelengths of light which are to be transmitted to a sample for analysis of the sample, optical fibers being used to transmit the selected wavelengths of light. Horvath et al, in U.S. Pat. No. 4,175,865, discloses a smoke detector which utilizes a plurality of optical fibers for detecting scattered smoke. In the Horvath et al patent, all optics are located within a single smoke detecting monitor. In U.S. Pat. No. 4,164,373, Schuss et al discloses an apparatus which utilizes optical fibers of differing length to provide a range of optical time delays for incident chromatic light pulses for the selective spatial and frequency analysis of light with a single detector.
It is to be noted that none of the patents noted above discloses the concept of utilizing optical fibers in a fire detection system to transmit a flame signal from a plurality of different locations to a single detector. The conventional fire detection systems described above also fail to envision the concept of utilizing optical fibers in a fire detection system to transmit a flame signal from a plurality of different locations to a single detector. The conventional fire detection systems, in contradistinction, utilize a plurality of detectors disposed at various monitoring locations, the detectors each being connected by electrically conductive wires to a central electronic analyzer, such systems having attendant expense and operational problems as described above. The present invention differs at a minimum from the conventional systems in the utilization of optical fibers to transmit a flame signal, thereby eliminating problems with EMI/RFI interferance which occur in the prior systems by virtue of the transmission of electrical signals of low magnitude. The further invention further obviates difficulties encountered by the penetration of fire extinguishing fluids into detectors at the remote monitoring locations as well as shorting caused by such contact in the electrical transmission portion of conventional systems.